The vet, named by Australian newspapers as Alister Rodgers, was transferred from Rockhampton Hospital to Royal Alexandra Hospital on Wednesday evening.
Dr Rodgers and three others considered most at risk of contracting the infection had not long completed an experimental five-day course of a hepatitis drug called ribavirin, which doctors had hoped would reduce the chances of the infection developing.
Meanwhile, the three others who also received ribavirin have been flown as a precautionary measure to Royal Alexandra Hospital for observation.
The Australian Veterinary Association (AVA) says vets are concerned for their sick colleague, whose life-threatening infection comes nearly a year to the day that Brisbane vet Ben Cunneen died from the virus, which is carried by native bats.
Association president Dr Mark Lawrie said that vets all around Australia are very anxious for the vet and his family, who have asked the public to respect their privacy.
"We've learned a lot about the virus in the 12 months since the tragic death of Ben Cunneen. There's been new research, and we've learned lessons from the last outbreak," he said.
"It's a terrible shock for the whole profession to have this happen again."
Dr Rodgers contracted the virus when treating a dying horse he initially suspected had suffered a snake bite.
"Vets in Queensland are taking the risk of Hendra virus very seriously and taking extra precautions when treating sick horses," Dr Lawrie said.
"It's not the time to discuss what has happened in this particular case. Right now, we want to do all we can to help him and his family. Before this, three out of the six people with the Hendra virus have died."
Dr Lawrie said that over the past year information has been made available to vets about how to take precautions.
"Government and leading research institutions have been disseminating the latest knowledge about the virus and advice for vets who treat horses through conferences, workshops and the internet.
"The AVA has also run professional seminars around Queensland for veterinarians and their staff about how to protect themselves from infection," Dr Lawrie said.
The Hendra virus is somehow transferred from bats to horses, althought the precise mechanism is not fully understood.
People are able to catch the virus if they have close contact with bodily fluids from an infected horse.
There are no known cases of human to human infection, nor any documented cases of people catching it directly off native fruit bats, although authorities advise people against handling the mammals.